1. Field of the Invention
The present invention relates to a method and a system for mounting electric components on a circuit substrate, and particularly to the improvements of the art of inspecting the state in which each electric component is mounted on the circuit substrate.
2. Related Art Statement
It has been practiced to inspect, when a plurality of electric components (xe2x80x9cECsxe2x80x9d) are mounted on a circuit substrate for producing an electric circuit, the state in which the ECs are mounted on the circuit substrate, for example, judge whether the ECs have been safely mounted on the circuit substrate, or whether the ECs have been mounted at appropriate positions or with appropriate attitudes on the circuit substrate.
ECs of a type which have no lead wires are temporarily attached to a circuit substrate with an adhesive or a solder paste, and then are finally fixed to the circuit substrate by hardening the adhesive or melting the solder paste. An EC mounting device mounts each EC on the adhesive or the solder paste applied in advance to each EC-mount portion of the circuit substrate. After all ECs are mounted on the circuit substrate, those ECs are finally fixed to the circuit substrate. An inspection is performed after the ECs are temporarily attached to the circuit substrate and/or after the ECs are finally fixed to the circuit substrate.
ECs of a type which have lead wires are temporarily attached to a circuit substrate by first inserting the lead wires through the holes formed in the circuit substrate and subsequently folding the lead wires onto the back surface of the circuit substrate, and then are finally fixed to the circuit substrate by soldering.
In either case, if an inspection is performed in the state in which the ECs are temporarily attached to the circuit substrate, the ECs can be finally fixed to the circuit substrate after an operator has solved the problems found by the inspection. Thus, the percentage of defective electric circuits can be reduced. Alternatively, the circuit substrate with which the problems are found can be discarded. In the latter case, the final fixing of the ECs to the circuit substrate can be omitted. Moreover, in the case where the problem that an EC is mounted with positional errors on a printed circuit board (xe2x80x9cPCBxe2x80x9d) in a temporary-attaching step can be distinguished from the problem that an EC is mounted with positional errors on a PCB in a final-fixing step, appropriate countermeasures can be taken to deal with those problems, respectively.
In the above-indicated background, U.S. patent application Ser. No. 09/015,521 assigned to the Assignee of the present application discloses a system which inspects, each time one EC is mounted on a circuit substrate, the state in which the one EC is mounted on the circuit substrate. More specifically described, immediately after each EC is mounted on the circuit substrate, the disclosed system takes the image of each EC and its vicinity, compares the taken image with a reference image pre-stored in a memory of the system, and judges whether each EC has been accurately mounted on the circuit substrate. Thus, the disclosed system does not need an inspecting device which is needed in the case where an inspection is performed after all ECs are temporarily attached to a circuit substrate, and which is provided at a position between an EC mounting device which temporarily attaches the ECs to the circuit substrate, and a final-fixing device such as an adhesive hardening furnace. Thus, the disclosed system can inspect the state in which each EC is mounted on the substrate, without increasing the total length of an electric-circuit assembly line or the production cost thereof.
It is therefore an object of the present invention to provide an electric-component mounting method and an electric-component mounting system which can inspect the state in which each electric component is mounted on a circuit substrate, with a higher reliability than that of the above-indicated prior system, or can employ a memory having a smaller capacity than that of the above-indicated prior system because of no need to store image data representing the reference image in the memory.
The present invention provides an electric-component mounting method and an electric-component mounting system which have one or more of the technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (12). Any technical feature which includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to that technical feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited.
(1) According to a first feature of the present invention, there is provided a method of mounting a plurality of electric components on a circuit substrate and thereby producing an electric circuit, comprising the steps of taking, immediately before each of the electric components is mounted on the circuit substrate, a first image of a first portion of the circuit substrate on which the each electric component is to be mounted and a second portion of the circuit substrate that is adjacent to the first portion, mounting the each electric component on the circuit substrate, taking, immediately after the each electric component is mounted on the circuit substrate, a second image of the mounted electric component and the second portion adjacent to the mounted electric component, and inspecting, by comparing the first and second images with each other, a state in which the each electric component is mounted on the circuit substrate. The timing of xe2x80x9cimmediately before each of the electric components is mounted on the circuit substratexe2x80x9d means a timing after the preceding electric component (xe2x80x9cECxe2x80x9d) has been mounted on the circuit substrate and before the each EC is mounted on the circuit substrate, or means, in the case where the circuit substrate is moved so as to be positioned relative to an EC mounting head (more strictly, an EC mounting position), a timing after the substrate has been positioned relative to the EC mounting head, for mounting of the each EC, and before the each EC is mounted on the circuit substrate. The timing of xe2x80x9cimmediately after the each electric component is mounted on the circuit substratexe2x80x9d means a timing after the each EC has been mounted on the circuit substrate and before the following EC is mounted on the circuit substrate, or means, in the case where the circuit substrate is moved so as to be positioned relative to the EC mounting head, a timing after the each EC has been mounted on the circuit substrate and before the substrate is moved so as to be positioned relative to the EC mounting head, for mounting the following EC. However, those timings do not mean a very short time before or after the mounting of each EC. In the case where an EC is mounted on a circuit substrate, a first image taken before the mounting of the EC and a second image taken after the mounting of the EC differ from each other. That is, the mounting of each EC influences the taken images. Comparing the two images with each other can lead to judging whether each EC has been safely mounted on the circuit substrate, or whether each EC has been accurately mounted on the first portion (i.e., EC-mount portion) of the circuit substrate. It is also possible to calculate positive and/or negative amounts of x-direction and y-direction positional errors of each EC mounted on the circuit substrate, and/or a positive or negative angular amount of rotation-position error of the mounted EC about an axis line passing through the center of the EC. One or more of those judging and calculating operations is or are one or more examples of the EC-mounting inspecting operation in which the first and second images are compared with each other. The present EC mounting method can enjoy a first advantage that the EC-mounting inspecting operation can be performed with improved reliability and/or a second advantage that a memory having a smaller capacity can be employed. The circuit substrate may have printed characters or lines, and/or may have one or more ECs which has or have already been mounted thereon. Although the images of the printed matters or the mounted ECs may be taken, both the first and second images taken before and after the mounting of each EC commonly include those background images. That is, the background images do not influence the comparison of the first and second images, and accordingly are not erroneously processed as the image of the EC in question. Thus, the present method can perform the EC-mounting inspecting operation with high reliability. In the case where an inspection is performed by comparing an image taken immediately after each EC is mounted on a circuit substrate, with a reference image stored in a memory, it is usual for the reference image to include an image of an EC but not to include any background images such as images of printed characters or lines. In this case, therefore, the background images make the taken image different from the reference image, thereby introducing an error into the inspection. In contrast, in the present method, two images are taken before and after the mounting of each EC and are compared with each other. Therefore, the present method can accurately recognize each EC and can perform a reliable inspection. In order to avoid an erroneous inspection, it is possible to employ a modified reference image including one or more background images such as images of printed characters or lines. However, it is cumbersome to prepare the modified reference image. The present method can improve the accuracy or reliability of inspection, while avoiding this problem. In addition, since the present method inspects the state in which each EC is mounted on the circuit substrate, by comparing the two images taken before and after the mounting of each EC with each other, the present method does not need pre-store, in a memory, a plurality of sets of image data representing different reference images corresponding to different sorts of ECs, in contrast to the case where an image taken after each of different sorts of ECs is mounted on the circuit substrate is compared with a corresponding one of different reference images pre-stored in a memory. Thus, the present method can employ a memory having a smaller capacity, which contributes to reducing the cost of production of an EC mounting system which performs the present method.
(2) According to a second feature of the present invention that includes the first feature (1), the step of taking the first image comprises taking the first image, using an image taking device, at a position relative to the circuit substrate, and the step of taking the second image comprises taking the second image using the image taking device at the position relative to the circuit substrate. In the case where an EC mounting head mounts each EC on the circuit substrate at a predetermined position and the circuit substrate is moved so as to be positioned relative to the EC mounting head, the image taking device can be provided at a position where the image taking device cannot be interfered with by the EC mounting head. In this case, it is not needed to move the image taking device relative to the circuit substrate. In the case where the circuit substrate is provided at a fixed position and an EC mounting head is moved so as to be positioned relative to the circuit substrate, it is preferred to employ a common moving device which moves both the image taking device and the EC mounting head. In the present method, the single image taking device suffices, which leads to reducing the cost of the inspection as compared with the case where two images are taken by different image taking devices before and after the mounting of each EC, respectively. In addition, since the two images before and after the mounting of each EC are taken from the same point of view, the two images are identical with each other except the absence or presence of each EC. Thus, the present method can perform an accurate inspection.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the step of mounting the each electric component comprising rotating a component holder which is rotatable about an axis line and which holds the each electric component, stopping the component holder at a predetermined component mounting position, moving the first portion of the circuit substrate to a position corresponding to the component mounting position, and mounting the each electric component on the first portion positioned at the component mounting position, and the steps of taking the first and second images comprise taking the first and second images in a state in which the first portion is positioned at the component mounting position. An image taking device may be used in such a manner that in the state in which an EC mounting head including the component (xe2x80x9cECxe2x80x9d) holder is stopped at the predetermined component (xe2x80x9cECxe2x80x9d) mounting position, the image taking device is moved to a position away from the EC mounting position and, after the EC mounting head is moved from the EC mounting position, the image taking device is moved to the EC mounting position. In this case, the image taking device can take each of the first and second images at a position right above the first portion of the circuit substrate. Alternatively, an image taking device may be provided at a position where the image taking device cannot be interfered with by an EC mounting head, as described above. In the latter case, it is not needed to move the image taking device. Thus, the image taking device can enjoy a simple construction. In addition, since no time is needed to move the image taking device, the present method can enjoy improved EC mounting efficiency.
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the step of taking the first image comprises taking, using an image taking device having a predetermined field of view, the first image at a timing before a component holder which holds the each electric component enters a predetermined image-process area included in the field of view of the image taking device, and the step of taking the second image comprises taking, using the image taking device, the second image at a timing after the component holder mounts the each electric component on the circuit substrate and exits from the image-process area. The image taking device may take an image at a position right above the first portion (i.e., EC-mount portion) of the circuit substrate, or in a direction inclined with respect to a straight line perpendicular to the circuit substrate. In the latter case, the image taking device may take an image in the state in which the component (xe2x80x9cECxe2x80x9d) holder is positioned at the position right above the EC-mount portion of the circuit substrate. When the EC holder which holds the EC is moved toward and away from the circuit substrate, the EC holder enters, and exits from, the image-process area included in the image-take area (i.e., field of view) of the image taking device. The image taking device takes an image currently present in its image-take area. The image-take area depends on the shapes and dimensions of an optical system and an image sensor or sensors of the image taking device. For example, in the case where an optical system defines a circular field of view and image sensors define a square field of view smaller than the circular field of view, the optical system and the image sensors define a square image-take area. In the case where the entire image (i.e., the entire image data) taken through the image-take area is processed, the image-take area is equal to the image-process area. On the other hand, in the case where only an image taken through a predetermined portion of the image-take area is processed, the predetermined portion is defined as the image-process area. If the image taking device takes the two images in the state in which the EC holder is positioned outside the image-process area, each of the two images does not include the image of the EC holder. Thus, the image of the EC holder is prevented from being erroneously processed as the image of each EC. Therefore, the present method can perform a reliable inspection. The size of the image-process area may be changed depending upon the size of ECs, or may be constant independent of the size of ECs. In the former case, the image taking device may take images at respective predetermined timings at which the image of the EC holder is not present in any sizes of image-process areas, or alternatively at respective timings that are changed depending upon the size of the current image-process area. In the present method, the image taking device takes the two images in the state in which the EC holder is not present in the image-process area. Thus, the present method can perform the inspection which is not adversely influenced by the image of the EC holder. In the particular case where the image taking device takes the two images at respective timings that are determined depending upon the size of the current image-process area, the present method can perform a reliable inspection without lowering the EC mounting efficiency.
(5) According to a fifth feature of the present invention that includes any one of the first to third features (1) to (3), the step of taking the first image comprises taking the first image at a timing at which the taken first image includes a third image of a component holder which holds the each electric component, and the step of taking the second image comprises taking the second image at a timing at which the taken second image includes a fourth image of the component holder which has mounted the each electric component on the circuit substrate, the fourth image included in the second image being substantially identical with the third image included in the first image. According to the present method, the image of the component (xe2x80x9cECxe2x80x9d) holder included in the first image taken before the mounting of each EC is substantially identical with the image of the EC holder included in the second image taken after the mounting of each EC. Therefore, the image of the EC holder is not erroneously processed as the image of each EC. Thus, the present method can perform an accurate inspection by comparing the first and second images with each other. The problem of whether respective images of the EC holder included in two two images are substantially identical with each other occurs only to the image-process area included in the image-take area (i.e., field of view) of the image taking device. However, if identical images of the EC holder are present in the image-take area at respective timings before and after the mounting of each EC, it is natural that identical images of the EC holder should be present in the image-process area at the two timings. The fifth feature (5) may be combined with the third feature (3), such that a portion of the movement of the EC holder toward or away from the circuit substrate and a portion of the movement of the substrate are concurrently performed. The first and second images are taken in the state in which the circuit substrate remains stopped. However, since each of the first and second images is permitted to include the image of the EC holder, the first image can be taken at a later timing before the mounting of each EC, and the second image can be taken at an earlier timing after the mounting of each EC, as compared with the case where the first and second images are not permitted to include the image of the EC holder. Thus, the movement of the circuit substrate can be stopped at a later timing, and can be started at an earlier timing, so that a portion of the movement of the EC holder and a portion of the movement of the substrate can be concurrently performed. Thus, for example, the circuit substrate can be moved for a longer time, can be moved at a lower velocity, acceleration, and deceleration, and can be started and stopped with less vibration. The ECs mounted on the circuit substrate are prevented from being moved out of position on the circuit substrate or falling off the substrate, and the vibration of the EC mounting system as a whole is effectively prevented. In the case where it is not needed to lower the velocity, acceleration, or deceleration of movement of the substrate, it is possible to shorten the cycle time of mounting of ECs (i.e., time needed for each EC to be mounted on the circuit substrate after the preceding EC is mounted on the circuit substrate) and thereby improve the efficiency of mounting of ECs. These advantages can be obtained not only when the fifth feature (5) is combined with the third feature (3) but also when the fifth feature (5) is applied to the case where the circuit substrate is moved along a first axis and the EC holder is moved along a second axis perpendicular to the first axis on a two-dimensional plane. The fifth feature (5) may be applied to the case where the circuit substrate is positioned and held at a fixed position, the EC holder is moved to any desired position along the plane of the substrate so as to mount each EC on the circuit substrate, and an image taking device is moved with the the EC holder. In this case, the image taking device takes images after the EC holder is moved to an EC mounting position and the image taking device is stopped. Since the first and second images taken by the image taking device are permitted to include the image of the EC holder, the first image can be taken at a later timing, and the second image can be taken at an earlier timing, as compared with the case where the first and second images are not permitted to include the image of the EC holder. Thus, the movement of the EC holder can be stopped at a later timing and can be started at an earlier timing, so that the EC holder can be moved for a longer time, or the cycle time of mounting of ECs can be shortened. In the case where the route along which the EC holder is moved toward the EC mounting position is different from the route along which the EC holder is moved away from that position, the EC holder is required to reach the EC mounting position and stop at that position, before the image taking device takes images. On the other hand, in the case where the EC holder is moved, after the mounting of each EC, in the opposite direction along the same route as that along which the EC holder holder is moved before the mounting of each EC, it is not essentially required that the EC holder be stopped at the EC mounting position before the image taking device takes images.
(6) According to a sixth feature of the present invention that includes any one of the first to fifth features (1) to (5), the step of inspecting the state comprises judging whether the each electric component has been mounted on the circuit substrate. When each EC is safely mounted on the circuit substrate, the second image taken after the mounting of each EC includes the image of the EC that is not included in the first image taken before the mounting of the EC. Thus, whether each EC has been mounted on the substrate can be judged by comparing the first and second images with each other. Whether each EC has been safely mounted on the circuit substrate may be inspected based on the shadow of the EC that is formed by a lighting device, as will be explained in the detailed description of the preferred embodiments, or may be inspected based on the image of the EC itself. In the former case, a reliable inspection can be performed even though the color of the EC may be very similar to that of the circuit substrate and the image of the EC may not be distinguished from that of the circuit substrate. The images may be chromatic or monochromatic.
(7) According to a seventh feature of the present invention that includes any one of the first to sixth features (1) to (6), the step of inspecting the state comprises judging whether the each electric component has been accurately mounted on the first portion of the circuit substrate. Whether each EC has been accurately mounted on the first portion of the circuit substrate may be judged by comparing the position of an electrically conductive pad which is provided on the circuit substrate and is to be electrically connected to the EC, and the position of the EC mounted on the circuit substrate.
One or more of the first to seventh features (1) to (7) of the EC mounting method may be combined with one or more of the eighth to twelfth features (8) to (12) of the EC mounting system that will be described below.
(8) According to an eighth feature of the present invention, there is provided an electric-component mounting system comprising a circuit-substrate supporting device which supports a circuit substrate; an electric-component mounting device which mounts a plurality of electric components on the circuit substrate supported by the circuit-substrate supporting device; an image taking device which takes, immediately before each of the electric components is mounted on the circuit substrate, a first image of a first portion of the circuit substrate on which the each electric component is to be mounted and a second portion of the circuit substrate that is adjacent to the first portion, the image taking device taking, immediately after the each electric component is mounted on the circuit substrate, a second image of the mounted electric component and the second portion adjacent to the mounted electric component; and an inspecting device which inspects, by comparing the first and second images with each other, a state in which the each electric component is mounted on the circuit substrate. The EC mounting device may comprise at least one EC holder which holds an EC. The EC holder may be one which is provided at a fixed position, or one which is moved, and is positioned at a predetermined position, by an EC-holder moving device. The EC-holder moving device moves the EC holder in at least one direction intersecting an axial direction parallel to an axis line of the EC holder, and positions the EC holder at the predetermined position. The EC-holder moving device may be one which includes a plurality of rotary members which are rotatable about a common axis line, independent of each other, and additionally includes a rotary-motion applying device which applies, to each of the rotary members, a rotary motion such that the each rotary member is fully rotated about the common axis, is stopped at least one time during its full rotation, and keeps a predetermined time difference from its preceding rotary member. Alternatively, the EC-holder moving device may be one which includes an intermittent-rotation body which is intermittently rotatable about an axis line and has a plurality of EC holders at respective equal distances from the axis line, and additionally includes a rotating device which intermittently rotates the intermittent-rotation body at an intermittent-rotation angular pitch equal to a spacing angular pitch at which the EC holders are equiangularly spaced from each other about the axis line. Otherwise, the EC-holder moving device may be one which includes a rotatable body which is rotatable about an axis line and has a plurality of EC holders on a circle whose center rides on the axis line, and additionally includes a rotating device which rotates the rotatable body by any desired angle in any desired direction. Moreover, the EC-holder moving device may be one which includes a movable member which has at least one EC holder, and additionally includes a movable-member moving device which moves the movable member in a direction perpendicular to an axis line of the EC holder. The movable-member moving device may be one which moves the movable member along a straight line, or along each of two straight lines perpendicular to each other on a two-dimensional plane. The above-described EC-holder moving device which includes the rotary members and the rotary-motion applying device, or the above-described EC-holder moving device which includes the intermittent-rotation body or the rotatable body and the rotating device may be provided on a movable member, and the movable member may be moved by a movable-member moving device. In the last case, the movable member and the movable-member moving device cooperate with the rotary members and the rotary-motion applying device, or the intermittent-rotation body or the rotatable body and the rotating device, to provide an EC-holder moving device. The circuit-substrate supporting device may have a construction corresponding to that of the EC mounting device. For example, the supporting device may be one which positions and holds the circuit substrate and moves the circuit substrate in two directions perpendicular to each other on a two-dimensional plane (e.g., a horizontal plane), one which moves the circuit substrate along a straight line, or one which positions and holds the circuit substrate at a fixed position. The EC mounting system according to the eighth feature (8) enjoys the same advantages as those of the EC mounting method according to the first feature (1).
(9) According to a ninth feature of the present invention that includes the eighth feature (8), the mounting system further comprises a lighting device which emits a light toward the circuit substrate in a first direction inclined with respect to a straight line perpendicular to a surface of the circuit substrate, and the image taking device is oriented toward the circuit substrate such that the image taking device takes the first and second images in a second direction inclined with respect to the straight line. The lighting device may be a slit-light emitting device which emits a flat, slit light, a columnar-light emitting device which emits a columnar light, or a radial-light emitting device which includes a point light source and emits a radial light. It is preferred that the slit-light emitting device or the columnar-light emitting device emit parallel light fluxes all of which are parallel to the optical axis thereof. For example, a columnar parallel light may be provided by a device including a semiconductor laser device and a beam expander, and a slit light may be provided by the columnar parallel light which passes through a slit. The radial-light emitting device may be obtained at the lowest cost. Excellent images can be obtained using a parallel light, and the thus obtained images can be easily processed. According to the ninth feature (9), the image taking device can take the image of each EC and its vicinity in the state in which an EC holder faces the first portion (i.e., EC-mount portion) of the circuit substrate. That is, the EC holder may not be moved away from the position opposed to the EC-mount portion, when the image-taking device takes an image. Thus, the present system can efficiently take the first and second images and inspect the state in which each EC is mounted on the substrate. In the case where each EC is lighted using a columnar light or a radial light whose cross section is much greater than the dimensions of the EC, the EC can be more reliably lighted than lighted using a slit light, even if respective upper surfaces of ECs mounted on the circuit substrate may have different heights because of different heights of the ECs or the warpage of the circuit substrate. In addition, the columnar light or the radial light is less likely to be completely interrupted by the ECs which have already been mounted on the circuit substrate, and the image of at least a portion of each EC can be taken and the state in which the EC is mounted on the circuit substrate can be inspected. According to the eighth feature (8), it is not essential to employ a lighting device. However, according to the ninth feature (9) wherein a lighting device is employed, clear images can be easily taken. In addition, in the case where the lighting device emits a light toward the circuit substrate in a direction inclined with respect to a straight line perpendicular to the circuit substrate, the shadow of each EC is surely formed on the circuit substrate. Thus, the present system can easily inspect the state in which each EC is mounted on the circuit substrate.
(10) According to a tenth feature of the present invention that includes the eighth or ninth feature (8) or (9), the electric-component mounting device comprises a plurality of component holders which hold respective electric components and which are rotated about a common axis line while being sequentially stopped at a predetermined component mounting position, the circuit-substrate supporting device comprises a circuit-substrate positioning device which positions the first portion of the circuit substrate at a position corresponding to the component mounting position, and the image taking device comprises a stationary image taking device which is provided in vicinity of the component mounting position.
(11) According to an eleventh feature of the present invention that includes any one of the eighth to tenth features (8) to (10), the inspecting device comprises means for judging whether the each electric component has been mounted on the circuit substrate.
(12) According to a twelfth feature of the present invention that includes any one of the eighth to eleventh features (8) to (11), the inspecting device comprises means for judging whether the each electric component has been accurately mounted on the first portion of the circuit substrate.